I hate to sound cynical but... 

You really should ask them to send you the cel 
back before you refund (or at least ask for a 
picture of the bend).  

If it's one thing e-Bay's tought me, it's that 
there are a LOT of opportunistic jerks out 
there.  It's great that you are willing to go 
the extra distance for a buyer (and I don't 
think there's ANY way it would be bad to buy 
them a replacement cel...if you're sure your cel 
was damaged)

You sound pretty sure you took good care of that 
cel and thought it was in good condition and 
also packaged it correctly, so I think it 
wouldn't be too out of line for you to ask for a 
little proof before going above and beyond the 
call of duty.  Especially if it was USPS's fault 
and not yours!